1. Field of the Invention
The present invention relates generally to medical guidewires. More particularly, the present invention relates to guidewires having hydrophilic coatings and methods for their fabrication.
Medical guidewires are used in a variety of procedures for guiding catheters and other devices to target sites within a patient's body. Of particular interest to the present invention, intravascular guidewires are used for the percutaneous introduction and guiding of both diagnostic and therapeutic catheters within a patient's vasculature. Such intravascular guidewires typically comprise a core wire formed from stainless steel, nickel-titanium alloy, tantalum, or other metals, and a coil tip disposed over the distal end of the core wire. The coil tip is typically a helically wound filament composed of a malleable metal which can be shaped by the physician in order to facilitate placement within the vasculature. After an initial puncture or cut-down is provided into the femoral or other access artery, the guidewire is advanced to the target location by pushing from the proximal end. The guidewire can also be twisted from the proximal end to properly position the bent or deflected coil tip in order to steer the guidewire through arterial junctions.
Guidewires have usually been coated with certain materials in order to facilitate placement through the vasculature. Initially, silicone, PTFE, and other lubricous (but non-hydrophilic) materials were applied both to the core wire and the coil tip in order to reduce friction between the guidewire and adjacent surfaces as the guidewire is introduced.
More recently, guidewires have been coated with hydrophilic materials which have proved to be superior to the earlier non-hydrophilic coatings discussed above. Hydrophilic coatings can trap a thin film of water on the surface of the guidewire, and the water film can prevent direct contact between guidewire and the vasculature and/or catheters which are introduced over the guidewire. Hydrophilic coatings are also more durable than the silicone coatings used previously.
While a significant advance in the design of guidewires, hydrophilic coatings suffer from certain drawbacks. In particular, hydrophilic coatings have generally not been applied to the coil tips of guidewires since they have a tendency to bind the coils together, rendering the coil too stiff and brittle for use. Thus, the advantages of hydrophilic coatings have been unavailable on the distal tip of the guidewire, where low surface friction is critical.
For these reasons, it would be desirable to provide improved guidewire designs and methods for their fabrication. In particular, it would be desirable to provide guidewires having coil tips, where the entire length of the guidewire including the coil tip is coated with hydrophilic coating. It would be particularly desirable if the hydrophilic coating on such guidewires would not significantly reduce the flexibility and shapeability of the coil tip. The methods for fabricating the wire should be relatively simple, compatible with a wide variety of hydrophilic materials, and result in hydrophilic coating having appropriate thicknesses and properties which are compatible with the intended use of the guidewire. At least some of these objectives will be addressed by the invention as described below.
2. Description of the Background Art
Guidewires comprising a core wire and a distal coil tip are described in U.S. Pat. Nos. 5,365,942; 4,964,409; 4,846,186; 4,748,986; 4,554,929; and 4,545,390. The '942, '186, and '929 patents each disclose coil tips having spaced-apart turns.
Catheters and guidewires having hydrophilic coatings are disclosed in U.S. Pat. Nos. 5,454,373; 5,443,455; 5,416,131; 5,242,428; 5,217,026; and 5,135,516; PCT Publications WO 93/10827 and WO 91/19756; and European Publications EP 661 072; and EP 591 091.
Guidewires which are encapsulated in plastic sleeves are disclosed in U.S. Pat. Nos. 5,452,726 and 5,333,620; and EP 661 073.
Methods and materials for hydrophilic coating of medical and other devices are described in U.S. Pat. Nos. 5,331,027; 5,067,899; 5,037,677; 5,001,009; 4,959,074; 4,801,475; and 4,663,233.